1. Field of the Invention
The present invention relates to a preload releasing fastener which may be used in systems which release such items as antennas, solar arrays, positioning mechanisms, and other devices.
2. Description of Related Art
A release apparatus may be used to release a captured member which constrains the deployment of a spacecraft element, such as a solar array and/or reflectors, in the stowed position. In many prior art devices, the spacecraft element was restrained with a wire or a holddown rod system which was released using a pyrotechnic device. Typically, the pyrotechnic device would fire an anvil against a base, with the wire or rod to be cut and released. Although useful in many applications, these devices imparted high shock loads into the units which they were to release, as well as the spacecraft itself. One aspect of the shock imparted into the system involves the shock due to the pyrotechnic device, and another aspect of the shock involves the sudden release of a tensioned system, and the motions involved therein. In some systems, the tensioned system release allows for quick motions of the release system, which are then constrained by motion limiters, and shocks are felt as the moving parts hit mechanical stops.
A design that avoided the shocks associated with pyrotechnic release devices was the separation spool device, which used a fused element to release a captured member. U.S. Pat. No. 6,133,818, to Baghdasarian, discusses a release apparatus wherein two piece split spool with an annulus is used to capture a capture member larger in diameter than the annulus of the spool. The two pieces of the split spool are held together with a wire that is wrapped around the spool.
However, other methods of reducing the shocks associated with releases of hold downs can be used.